While Trump's image hasn't improved appreciably for months -- and he remains the most unpopular presidential nominee in modern history -- Clinton continues to see her own image decline. It's now at its worst point ever and, according to a Washington Post-ABC News poll of registered voters, basically as bad as Trump's.

And the reason is clear: The email story is absolutely killing her -- and ruining what might otherwise be a coronation.

A new CNN/ORC poll demonstrates it pretty clearly. While polls at the start of the 2016 race showed Americans were basically split about whether her use of a private email server gave them pause about voting for her, it's now clear that it's a significant hurdle for a strong majority of Americans in voting for Clinton.

The poll shows fully 62 percent of registered voters agreed with the statement that her use of the server is "an important indicator of her character and ability to serve as president." That number has risen steadily this year, from 46 percent in March 2015, to 55 percent in October, to 58 percent in June 2016, and now to 62 percent today.

Just 36 percent say the email server is "not relevant to her character or her ability to serve as president." That's down from 52 percent at the start of the campaign 18 months ago.

Behold the steady decline:

The difference between now and before? While before people generally agreed that the server was a bad idea but were split along partisan lines about whether it was actually relevant, the issue seems to have moved steadily from being a nuisance for Clinton to a genuine -- and growing -- liability.

In March 2015, a CBS News poll showed 62 percent thought the server was "inappropriate." An August 2015 CNN poll showed 56 percent thought she did something wrong.

But polls last year also suggested it was just another issue for partisans. An October NBC/Wall Street Journal poll showed 47 percent of voters said it was an important factor in their vote, while 44 percent said it was not. The same CBS poll in March 2015 showed just 29 percent said it diminished their view of her -- compared to 65 percent who said it had no effect.

At this point, it's hard to point to basically any other major explanation for Clinton's declining poll numbers and the tightening overall race. She's run a largely quiet campaign until this past week and has been content to let Trump make the news. The one constant story about Clinton has been new revelations about her emails and the Clinton Foundation (which the new poll, by the way, shows 60 percent say should be shut down either now or if she becomes president). And if you look closely, perceptions about her email server track closely with her overall image and her perceived honesty and trustworthiness.

The FBI Sept. 2 published a detailed report on its investigation into Democratic presidential candidate Hillary Clinton's use of a private email server while she was secretary of state. On Oct. 28, FBI director James Comey announced it would conduct a new investigation. (Sarah Parnass/The Washington Post)

Democrats clearly think the email issue is overblown. They cried foul when Clinton was asked about it for a large chunk of her 30 minutes at Wednesday night's NBC Commander-in-Chief Forum.

Judging by the amount of time NBC’s Matt Lauer spent pressing Hillary Clinton on her emails during Wednesday’s national security presidential forum, one would think that her homebrew server was one of the most important issues facing the country this election. It is not. There are a thousand other substantive issues — from China’s aggressive moves in the South China Sea to National Security Agency intelligence-gathering to military spending — that would have revealed more about what the candidates know and how they would govern. Instead, these did not even get mentioned in the first of 5½ precious prime-time hours the two candidates will share before Election Day, while emails took up a third of Ms. Clinton’s time.

People are welcome to make their own judgments about just how important this issue is and whether it deserved so much time, given the constraints of the forum Wednesday. For a growing segment of voters that now numbers about 62 percent, though, it is an important issue.

And it's arguably turned what might otherwise have been a pretty easy win for Clinton into something else emtirely.